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| swiss:
Hello everyone, We currently suspect that some of the cr2032 button batteries we receive do not meet the specifications. We would therefore like to buy a setup where we can check the capacity and internal resistance of individual cells. The solution should not cost more than 2000 USD. Can you recommend something? |
| TERRA Operative:
Any DC load that can apply a constant load with data logging features should do it, yeah? Hook up the battery and test using the relevant standardised test if there is one, or the parameters in the datasheet from the manufacturer. Even an ebay or Aliexpress special would be capable of doing this sort of test. Heck, even a mosfet on a heat sink with a couple multimeters with logging would work. |
| Fungus:
--- Quote from: TERRA Operative on November 09, 2023, 07:00:01 am ---Even an ebay or Aliexpress special would be capable of doing this sort of test. Heck, even a mosfet on a heat sink with a couple multimeters with logging would work. --- End quote --- An Arduino and a 10k load resistor...? |
| robert.rozee:
--- Quote from: swiss on November 09, 2023, 06:20:40 am ---We currently suspect that some of the cr2032 button batteries we receive do not meet the specifications. --- End quote --- i take it the devices these cells are being used in is a DM15L or similar calculator? one problem you may be encountering (if this is the case) is high intermittent current draw pulling down the cell voltage to the point of (a) resetting the calculator and/or (b) generating waste heat within the cell (waste heat = lost energy). most lithium button cells are rated for a relatively low current draw (a few mA) and with any higher current draw the usable cell capacity will be diminished. therefore in a specific user-case cr2032 brand A versus cr2032 brand B may have vastly different usable lifespan in your application, whereas on paper and under standardized testing perform identically. your best bet would use the actual device (DM15L) as the load, running custom software to keep it 'exercising' the cell to simulate typical usage. a simple DMM performing data logging, attached to a PC, can then monitor battery voltage. something like an HP34401A set to read cell voltage continuously and outputting data via the serial port would suffice. then use almost any terminal program to log data to a file for examination in Excel / Libre Office Calc. cheers, rob :-) |
| Ian.M:
You don't have the budget for pro grade equipment to do this job (e.g. a Keithly SMU would be an order of magnitude more expensive) so will almost certainly need to DIY, as hobby grade battery discharge testers capable of detailed logging are typically intended for far higher capacity batteries, so cant provide a suitable load. Look at the battery datasheets! If you want to reject out-of-spec cells, you need to test with the manufacturer's specified load, not your device's actual load current. However if your device exceeds the highest pulsed load in the datasheets of good quality branded cells, you have a problem! Most if not all the datasheets seem to show data for resistive loads rather than constant current loads, and the lowest resistance pulsed load I have seen is 100 ohms for an Energiser CR2032. I agree with Fungus: use an Arduino or similar. The higher resistance continuous loads could be directly switched by MCU I/O pins sinking their current, but anything under 1K is going to need a small MOSFET, with its gate driven by the I/O pin. If the load resistance is accurately known, the discharge current can be calculated from the terminal voltage, and an AVR Arduino's ADC would be good enough, if buffered by a unit gain OPAMP so its sampling current doesn't load the cell under test. If you want a standalone unit consider hacking a M328 style component tester kit. Fit your discharge resisters in place of the kit's resistors between the MCU and the test pins, hack in an OPAMP buffer in one of the ADC inputs from the test pins, and hack the other two to drive MOSFETs for the low ohm pulsed loads, link all the test pins together and connect the cell holder between there and ground. For firmware development purposes it can be treated as an Arduino with no bootloader. |
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